Age Matters When It Comes To Marijuana Use, But Context Matters To Understand Why

The age at which someone first begins smoking marijuana could make a big difference in their future drug use, suggests a new study. But context always matters – and in the case of this research, understanding the context in which someone starts using marijuana is essential to understanding the results.

The study analyzed data for 1,030 boys who were part of the Montreal Longitudinal and Experimental Study, a study of kids from low-income white neighborhoods that started in the early 1980s. Researchers asked the study participants every year between the ages of 13 and 17 if they’d smoked marijuana anytime during the previous year. Beginning at age 17, they also asked them if they’d taken other drugs in addition to pot – namely cocaine, speed, heroin, hallucinogens, depressants, and a variety of others. Those questions were revisited at ages 20 and 28. (Since this study involved people answering questions about their drug use, it’s a given that not everyone responded truthfully, but let’s assume enough of them fessed up to make the analysis worthwhile.)

The results showed that the younger the boys started smoking pot (specifically before age 15), the more likely they were to develop a drug problem by their late 20s. Just a year or two made all the difference – when pot use started after 15, the risk of future drug abuse was much lower.

"The odds of developing any drug abuse symptoms by age 28 were non-significant if cannabis use had its onset at ages 15 to 17, but were significant and almost doubled each year if onset was before age 15," quoting from the study.

At first glance, the results sound like confirmation of the old “gateway drug” theory that using pot leads to abuse of harder drugs, but the rest of the story provides important context. The study also found that the kids most likely to smoke pot before age 15 were also most likely to get involved with gangs, commit crimes like vandalism and drink alcohol.

In other words, smoking pot was just one element of a bigger behavioral mess that set the stage for drug abuse. Importantly, if the same kids were also drinking by age 17, they were far more likely to be alcoholics by 28.

Frequency of use also mattered. From the study: “Even if those who start smoking cannabis at 17 years were at lower risk, frequent users (20 or more times a year) at age 17 had almost double the chance of abuse by age 28 than occasional users.”

More than telling us something new about a link between marijuana use and subsequent drug abuse, the results reinforce an important understanding about the strength of behaviors that begin in early adolescence. A wealth of research already backs that up, and all of it speaks to the critical importance of focusing attention on the formative period when entrenched patterns of behavior start taking shape.

Do the study results offer cause for concern about when marijuana use begins? Yes. But more broadly they add to what we know about the potential outcomes of risky behavior starting early in life. These are, however, behavioral correlations, not guarantees of how a life will turn out, and they can be changed.